1. Field of the Invention
The present invention relates to a substrate structure made mountable under a high temperature environment. For example, the invention relates to a substrate structure enabling to be mounted at inside of a housing of a transmission in a vehicle.
2. Description of the Related Art
A description will be given of a technology related to the invention in reference to the drawings as follows.
FIG. 3 is a view showing a conventional substrate structure 100.
As shown by FIG. 3, the substrate structure 100 generally used conventionally comprises a pattern 140 forming a circuit. The pattern 140 is formed by an etching process or the like on a surface of a substrate 110. The substrate 110 is made of a glass epoxy material or the like and formed in multiple layers. A mounted part 120 is mounted via a solder 150 in accordance with the pattern 140. A mounting method for mounting the mounted part 120 is provided, in which solder paste is coated on a portion on the pattern 140 to which the mounted part 120 is intended to mount. Then, the mounted part 120 is mounted thereon, and the substrate 110 is subjected a high temperature environment of a reflow furnace or the like to thereby solidify the solder paste, or the like.
Further, when the mounted parts 120 are mounted on both faces of the substrate 110, a through hole 130 penetrating the substrate 110 from its upper face to its lower face, is provided at the substrate 110. Then, an electrically conductive portion 160 is formed by adhering copper onto a surface of an inner portion of the through hole 130 to thereby conduct the patterns 140 provided at the upper face and the lower face of the substrate 110.
However, the above-described substrate structure is formed persistently on the premise that the substrate structure is mounted under a normal environment. For example, the substrate structure is generally formed even when the substrate structure is subjected to thermal cycle of 3000 cycles under surrounding temperature of xe2x88x9230xc2x0 C. through 80xc2x0 C., or when subjected under an environment at surrounded temperature of 105xc2x0 C. for 1000 hours.
Accordingly, when the substrate structure is mounted under an environment deviated from a range of such an environment set as described above, for example, mounted under an environment in which surrounding temperature exceeds the set environment as in a housing of a transmission in a vehicle (surrounding temperature is about 120xc2x0 C.), the following problem would arise.
According to the conventional substrate structure, pattern arrangement on the surface of the substrate is complicated. Therefore, there is a possibility of generation of short circuit in the circuit due to dew condensation or the like. A resist film is provided to cover the patter nor the solder in order to prevent the possibility. However, such a resist film does not withstand under the above-described high temperature environment, and therefore, break is caused. Further, there poses a problem that when break is caused in the resist film, break is caused also in the pattern and the solder covered by the resist film.
Further, linear expansion coefficients by heat of the substrate formed by the glass epoxy material are as much as 14 ppm in the horizontal direction (longitudinal direction of substrate) and 50 ppm in the vertical direction (thickness direction of substrate). Therefore, when a bare chip is mounted on the surface of the substrate, there poses a problem that break is caused at a connected portion between an electrode of the bare chip and the substrate by thermal stress in the horizontal direction. Further, when the through hole is provided in the substrate, break is caused at an electrically conductive portion on the surface of the inner portion of the through hole by thermal stress in the vertical direction.
Further, high temperature resistance of the glass epoxy material per se falls in a range of 120 through 130xc2x0 C. and accordingly, there poses a problem that the substrate per se is softened under a high temperature environment at temperatures equal to or higher than 120xc2x0 C.
Further, with regard to a substrate structure withstanding even under such a high temperature environment, conventionally, there has been conceived a method of forming a substrate not by a glass epoxy material but by a ceramic material excellent in high temperature resistance against heat and having a low linear expansion coefficient. According to the method, the linear expansion coefficient of the substrate per se is low. A pattern formed on the surface of the substrate can be formed by a sintering process. Accordingly, the problem is not posed in the case of the above-described glass epoxy material, and the substrate can be mounted even under the high temperature environment.
However, according to the substrate structure using the ceramic material, in comparison with the substrate structure using the normal glass epoxy material, there poses a problem that the cost is increased significantly.
The invention has been made to resolve the above-described problems. It is an object thereof to provide a substrate structure capable of being mounted under a high temperature environment at low cost.
According to the present invention, there is provided a substrate comprising:
a first substrate;
a second substrate disposed on the first substrate, the second substrate having a first circuit pattern;
a third substrate disposed on the second substrate, the third substrate mounting thereon a part having an electrode;
a part pad provided on the third substrate to correspond to the electrode of the part; and
an electrically conducting member disposed in the third substrate and right under the part pad, the electrically conducting member electrically connecting the part pad and the circuit pattern of the second substrate.
In the substrate structure, the third substrate may have a hole formed right under the part pad;
an electrically conductive paste may form the electrically conducting member; and
the electrically conductive paste may be filled with in the hole to electrically connect the part pad with the electric pattern of the second substrate.
In the substrate structure, the first to third substrates may comprise a resin material.
In the substrate, wherein all of the circuit pattern may be formed between the first and second substrates and between the second and third substrates. In the substrate, the second substrates may comprise:
a fourth substrate disposed on the first substrate;
a fifth substrate disposed on the fourth substrate; and
a sixth substrate disposed on the fifth substrate.
In the structure, the third substrate may be disposed on the sixth substrate.
In the structure, the second circuit pattern may be formed between the third and sixth substrates and electrically connected with a battery.
A third circuit pattern may be formed between the first and fourth substrates and grounded.